With the development of orthodontic brackets such as those described, for example in U.S. Pat. No. 4,068,379, orthodontic brackets have replaced bands as the primary appliance for connecting orthodontic archwires to teeth. Unlike the banded appliances in which archwire supports mounted on bands that encircle teeth to hold the archwire supports in place on the teeth, brackets rely solely on an adhesive bond between the base or pad of the bracket and the surface of the crown of the tooth. Adequate bond strength between the teeth and the bracket bases has traditionally required the doctor or an assistant to dispense adhesive onto the bracket at chairside, using single or multiple part dental adhesives specifically developed for securing orthodontic appliances to teeth. Popular single part adhesives are cured by ultraviolet light, while multiple part adhesives cure chemically, following the mixing of the adhesive immediately preceding its use. The multiple part adhesives are often capable of producing bonds that are stronger than with the light cured adhesives.
The application of adhesives to brackets at chairside is a time consuming requirement. In preparing the adhesive at chairside, the quantity of adhesive dispensed must be carefully controlled by office personnel. Cleanup is required, which must be done by the doctor whose time is expensive. The handling of brackets during the application of adhesive can result in misorientation of the appliances and a mixup of the appliances, which are usually designed to fit specific teeth.
One attempt to minimize the chairside handling of adhesives in the application of orthodontic appliances to teeth has been the introduction of orthodontic brackets with light cured adhesive pre-applied to the bracket bases. While these brackets with pre-applied adhesive are attractive to orthodontists for their promise of convenience and ease of installation on the teeth of the patient, such brackets have been associated with an increased failure rate of the bond between the bracket bases and the teeth.
One cause of failures of the bonds between the bracket and a tooth is due to the use of an adhesive beyond its actual shelf life. The shelf life of adhesive that has been pre-applied to brackets is optimistically claimed to be twenty-four months. In practice, environmental factors, such as heat, humidity, etc., during transit and storage of the brackets having the pre-applied adhesives, shortens the shelf life of the adhesive. Furthermore, orthodontic brackets with adhesives pre-applied seldom reach the offices of orthodontists immediately following manufacture, so that some portion of the shelf life of the adhesive is already spent by the time the brackets are received by the orthodontist. In addition, careful records and careful inventory control by the doctor is required to insure that all adhesively pre-coated brackets are used in a FIFO basis and before the adhesive becomes too old.
Orthodontic brackets are often stocked by orthodontists in sufficient quantities so that the doctor has available appliances of various types and sizes to use on any common occasion in the treatment of patients. Maintaining appliance inventories necessarily requires that certain appliances will be in inventory longer than others. Ordinarily, orthodontic brackets are made of metal or other materials that have a shelf life that exceeds the technological life of the appliance, that is, the appliance can usually be stored until it is used or becomes obsolete, which can be many years from the stocking of the appliance by the doctor. Orthodontic brackets have a cost of several dollars to the doctor, for example, four U.S. dollars per bracket at the time of this patent application. The cost of the adhesive used to secure orthodontic brackets to teeth is substantially less expensive than the ordinary bracket, from a few cents to about a seventy-five cent per bracket price premium charged by an adhesively pre-coated bracket manufacturer. As a result, the application of a few cents worth of adhesive imposes a limited shelf life on a relatively expensive orthodontic appliance.
There are additional disadvantages to the adhesively pre-coated orthodontic appliances currently available on to orthodontists. The packaging of such appliances, for example, is quite expensive to produce and bulky. One hundred cases, for example, might occupy several cubic feet of space in a dentist office, equal, for example, to that of a small appliance or piece of furniture. Individual brackets are packaged in sealed packages which must be individually opened at chairside. Appliance delivery systems cannot readily accommodate these brackets or bracket packages, and separate systems for dispensing adhesive primer must be used. Only one part, light curable adhesives, can be pre-applied to brackets. Use of multiple part adhesives, which can be up to thirty percent stronger, are not practical with such brackets. Furthermore, when the amount of pre-applied adhesive appears to be incorrect in a particular situation, there is no easy way to adjust the quantity.
Accordingly, there is a great need on the part of orthodontic practitioners for a system for easily and conveniently applying orthodontic appliances to teeth with adhesive that does not have all of the disadvantages of the pre-adhesively coated orthodontic brackets of the prior art.